Fundamental Units involved in Energy Measurements

Power = Energy/Time
SI unit of power is watt and that of energy is joule  (1 watt = 1 joule/sec)
The electricity is usually expressed in terms of power as Megawatts (MW)
1 MW = 1,000,000 W = 1,000,000 J/s

The electricity is also commonly expressed in terms of energy as kilowatt-hour
1 kilowatt-hour is the energy when 1 kilowatt (1000 W) power is produced for 1 hour
i.e., 1 kWH = 1000 W x 3600 s = 3,600,000 J = 3600 KJ

Energy is also commonly expressed as calorie.  A calorie is the amount of energy required to raise the temperature of 1 gm of water by 1 oC
1 calorie = 4.184 joules

Another commonly used unit is British thermal unit (Btu).  A Btu is the amount of energy required to raise the temperature of 1 pound of water by 1 oF 
1 Btu = 1055.06 joules
100,000 Btu = 1 therm

Approximate Cost:  $0.15 per kwh (May change significantly based on location and season of use).

Appliance	watt	Hours/Day	kwh
40-49 in Plasma	400	4	1.6
Dishwasher	1200	1	1.2
Refrigerator	500	10	5.0
Dryer	5000	0.5	2.5
Washer	500	0.5	0.25
Water Heater	4500	2.5	11.25
Computer	300	8	2.4
Portable Heater	1500	4	6.0